This invention generally relates to a vehicle motion control system. More particularly, the present invention pertains to a vehicle motion control system which supplies hydraulic pressure generated by an automatic hydraulic pressure generator, capable of generating hydraulic pressure irrespective of a brake pedal operation, to a wheel brake cylinder via a control valve. This vehicle motion control system is applicable to a brake steering controller (a controller for preventing vehicle lateral skidding) and to a traction controller.
A known type of vehicle motion control system is described in Japanese Patent No. 2790288 issued in 1998, and U.S. Pat. No. 4,966,248. In this vehicle motion control system, a switching solenoid valve is connected to a vacuum servo unit or vacuum booster. The switching solenoid valve is capable of being selectively switched between either a non-operative position in which a servo unit does not operates when a brake pedal is not depressed or an operative position in which a vacuum servo unit operates independently when the brake pedal is not depressed. During an acceleration slip of the driving wheels (i.e., during a traction control), the switching solenoid valve is switched to the operative position, the vacuum servo unit is operated, and a master cylinder generates a hydraulic pressure without any brake pedal operation. The master cylinder hydraulic pressure is controlled by a modulation unit (a hydraulic pressure control valve) and is supplied to a wheel brake cylinder of a driving wheel which is experiencing acceleration slipping.
The known system described above suffers from several drawbacks. Because the switching solenoid valve is maintained at the operative position during traction control, the hydraulic pressure generated in the master cylinder could exceed the hydraulic pressure that the traction control requires when a negative pressure supplied to a constant pressure chamber of the servo unit changes. An undesired switching noise is generated when a hydraulic brake pressure of a wheel brake cylinder is adjusted by the modulation unit in the above situation.
The switching noise is generated when the fluid communication between the master cylinder and the wheel brake cylinder is switched from the open to closed condition by the modulation unit while excessively high master cylinder hydraulic pressure exists. Also, when the fluid communication between the master cylinder and the wheel brake cylinder is switched from the closed to the open condition, a switching noise is generated by the differential pressure between the master cylinder and the wheel brake cylinder. Likewise, a switching noise is generated when the connection between the wheel cylinder and the reservoir is opened or closed by the modulation unit.
The phenomenon mentioned above occurs remarkably when the known vehicle motion control system is applied to a control for preventing vehicle lateral skidding because the hydraulic pressure necessary for the vehicle lateral skidding control is high.
In light of the foregoing, a need exists for a vehicle motion control system which generates less switching noise when the hydraulic pressure valve is switched while the motion control is under operation.
The present invention provides a vehicle motion control system that includes a wheel brake cylinder disposed on a wheel to supply a braking force to the wheel, an automatic hydraulic pressure generator which generates hydraulic pressure irrespective of brake pedal operation, a hydraulic pressure control valve disposed between the automatic hydraulic pressure generator and the wheel brake cylinder to adjust the hydraulic brake pressure of the wheel brake cylinder by controlling fluid communication between the automatic hydraulic pressure generator and the wheel brake cylinder, and a braking controller for performing the motion control by actuating the hydraulic pressure control valve in accordance with the motion condition of the vehicle. A hydraulic pressure detecting device detects the generated hydraulic pressure of the automatic hydraulic pressure generator, and a braking control mechanism includes a necessary hydraulic pressure setting device for setting a hydraulic pressure required for the motion control in accordance with the vehicle motion condition during the motion control, and a hydraulic pressure adjusting device for controlling the automatic hydraulic pressure generator and adjusting the generated hydraulic pressure thereof in accordance with the compared result of the actually generated hydraulic pressure of the automatic hydraulic pressure and the required pressure for the motion control.
The motion control system can also include a brake steering control, or control for preventing a vehicle lateral skidding, a traction control and an automatic brake control (a control of the distance between moving vehicles).
The system of the present invention is capable of reducing the switching noise generated when the hydraulic pressure control valve is switched. This is because the generated hydraulic pressure of the automatic hydraulic pressure generator is regulated to the level of the necessary hydraulic pressure for the motion control by adjusting the generated hydraulic pressure of the automatic hydraulic pressure generator in accordance with the comparison between the necessary hydraulic pressure for the motion control and the actually generated hydraulic pressure of the automatic hydraulic pressure generator.
Because the automatic hydraulic pressure generator is controlled in accordance with the result of the comparison between the necessary hydraulic pressure for control and the generated hydraulic pressure of the automatic hydraulic pressure generator, the operation frequency of the hydraulic pressure controller can be reduced. Thus the generation frequency of the switching noise can be reduced.
The necessary hydraulic pressure setting device sets the necessary hydraulic pressure of each wheel in accordance with the vehicle motion attitude during the motion control. Preferably, the hydraulic pressure adjusting device controls the automatic hydraulic pressure generator to adjust the generated hydraulic pressure in accordance with the comparison between the generated hydraulic pressure of the automatic hydraulic pressure generator and the maximum value of the necessary hydraulic pressure of a plurality of controlled wheels. The necessary hydraulic pressure is supplied to all of the controlled wheels securely because the generated hydraulic pressure of the automatic hydraulic pressure generator is adjusted in accordance with the result of the comparison between the generated hydraulic pressure of the automatic hydraulic pressure generator and the maximum value of the necessary hydraulic pressure of a plurality of the controlled wheels.
It is preferable that the hydraulic pressure adjusting mechanism is adapted to control the automatic hydraulic pressure generator to make the generated hydraulic pressure of the automatic hydraulic pressure generator correspond to the necessary hydraulic pressure of the controlled wheels. The switching noise generated when the hydraulic pressure control valve is switched and the frequency of generation of the switching noise can thus be reduced. Further, the necessary hydraulic pressure for the motion control can thus be supplied to the controlled wheels.
It is also preferable that the necessary hydraulic pressure setting device is adapted to set the necessary hydraulic pressure for the motion control for every motion control action, and to calculate the maximum value of a plurality of the necessary hydraulic pressures when a plurality of the motion controls are performed to the vehicle. Also, the hydraulic pressure adjusting device is adapted to adjust the generated hydraulic pressure of the automatic hydraulic pressure generator in accordance with the result of the comparison between the generated hydraulic pressure of the automatic hydraulic pressure generator and the maximum value of a plurality of the necessary hydraulic pressures. When the plurality of the motion controls are performed with respect to the vehicle, a plurality of motion controls are appropriately performed because the generated hydraulic pressure of the automatic hydraulic pressure generator is adjusted in accordance with the result of the comparison between the automatic hydraulic pressure generator and the maximum value of the plurality of necessary hydraulic pressures.
The brake controller includes a traction control device and a brake steering control device. The traction control device applies braking torque to a driving wheel by controlling the hydraulic pressure control valve in accordance with the acceleration slip condition of the driving wheel of the vehicle during the vehicle acceleration. The brake steering control device applies at least one wheel of the vehicle a braking force by controlling the hydraulic pressure control valve in accordance with the tendency of an oversteering or understeering condition of the vehicle. The necessary hydraulic pressure setting device sets the necessary hydraulic pressure for the traction control in accordance with the acceleration slip condition during the traction control and sets the necessary hydraulic pressure for each controlled wheel in accordance with the tendency of the oversteering or understeering condition of the vehicle during the brake steering control. In addition, the necessary hydraulic pressure setting device calculates the maximum value of the necessary hydraulic pressures of the brake steering control wheels set for each wheel and the necessary hydraulic pressure of the traction control. The hydraulic pressure adjusting device is adapted to adjust the generated hydraulic pressure by controlling the automatic hydraulic pressure generator in accordance with the result of the comparison between the generated hydraulic pressure of the automatic hydraulic pressure generator and the maximum value of the necessary hydraulic pressure.
When both traction control and the brake steering control to the vehicle are performed, the generated hydraulic pressure of the automatic hydraulic pressure generator is compared to the maximum value of the necessary hydraulic pressure of the brake steering control wheel, and the generated hydraulic pressure of the automatic hydraulic pressure generator is adjusted in accordance with the result. As a result, the traction control and the brake steering control are performed appropriately.
The automatic hydraulic generating device includes a master cylinder, a vacuum booster, and a switching solenoid valve. The master cylinder generates the hydraulic pressure corresponding to the depression force of the brake pedal. The switching solenoid valve is capable of selectively being switched to either a non-operative position in which the vacuum booster is not actuated or an operative position in which the master cylinder is operated by the actuation of the vacuum booster at least partially irrespective of the operation of the brake pedal. The hydraulic pressure adjusting device is adapted to adjust the master cylinder hydraulic pressure by controlling the switching solenoid valve in accordance with the result of the comparison between the master cylinder hydraulic pressure and the controlled wheels. A brake control actuator of the motion control device can thus be produced at a low cost.
The vacuum booster is comprised of a movable partition, a constant pressure chamber, a variable pressure chamber, a valve mechanism, an auxiliary movable partition, and an auxiliary variable pressure chamber. The constant pressure chamber is formed in front of the movable partition, and negative pressure is introduced into the constant pressure chamber. The variable pressure chamber is formed in back of the movable partition, and is set to select either the condition in which it is connected to the constant pressure chamber for introduction of negative pressure or the condition blocked from the constant pressure chamber and exposed to the atmosphere. The valve mechanism opens and closes the communication between the constant pressure chamber and the variable pressure chamber, and the connection between the variable pressure chamber and the atmosphere. The auxiliary movable partition is disposed in the constant pressure chamber, actuates the master cylinder in accordance with the depression of the brake pedal, and drives the master cylinder when the brake pedal is not operated. The auxiliary variable pressure chamber is formed between the auxiliary movable partition and the movable partition. Preferably, the switching solenoid valve is adapted to switch between an operative position that exposes the auxiliary variable pressure chamber to the atmosphere and a non-operative position that introduces negative pressure to the auxiliary variable pressure chamber.
According to another aspect of the invention, a vehicle motion control system includes a wheel brake cylinder for applying a braking force to a wheel, an automatic hydraulic pressure generator which generates a hydraulic pressure including during non-operation of a brake pedal, a hydraulic pressure control valve disposed between the automatic hydraulic pressure generator and the wheel brake cylinder to adjust hydraulic brake pressure supplied to the wheel brake cylinder by alternatively connecting and disconnecting at least the automatic hydraulic pressure generator and the wheel brake cylinder, a hydraulic pressure detector for detecting a generated hydraulic pressure of the automatic hydraulic pressure generator, and a brake controller for performing vehicle motion control by controlling at least the hydraulic pressure control valve in accordance with a motion condition of the vehicle. The brake controller includes a necessary hydraulic pressure setting mechanism for setting a necessary hydraulic pressure that is necessary for effecting the motion control in accordance with the motion condition of the vehicle and a comparing mechanism for comparing the necessary hydraulic pressure set by the necessary hydraulic pressure setting mechanism with the generated hydraulic pressure detected by the hydraulic pressure detecting mechanism. A hydraulic pressure adjusting device adjusts the generated hydraulic pressure of the automatic hydraulic pressure generator based on the results of the comparison between the necessary hydraulic pressure and the generated hydraulic pressure.